All of my prior applications and patents above identified disclose certain features of energy conversion systems adapted to increase the efficiency of energy conversion, particularly the efficiency of conversion of energy of gaseous fuels such as natural gas; and all of said prior applications and patents disclose certain heat exchanger devices adapted to increase the efficiency of heat transfer from the products of combustion of petroleum fuels, especially natural gas, to fluids, particularly liquids such as water. In all of said prior applications and patents heat exchanger devices are disclosed and such devices are arranged to provide for indirect heat transfer from the products of combustion to the liquid or other fluid to be heated by means of tube-in-tube type heat exchangers in which conditions are established providing for cooling of the combustion products to a temperature below the dew point, in order to utilize the large amount of BTU's released upon condensation of the water vapor present in the products of combustion.
The present application also contemplates highly effective recovery of the BTU's by establishing conditions which will reduce the temperature of the products of combustion to a temperature below the dew point, before discharge of the gaseous products of combustion. The present invention, however, is concerned with a combination of a number of improvements and features which further enhance the efficiency and which also provide numerous additional advantages, most of which are described hereinafter in relation to individual embodiments of the equipment herein disclosed.
Before proceeding with more detailed description of the structural embodiments and features and advantages of the operation of systems according to the present invention, it is here first pointed out that while certain aspects of the invention are adaptable to use with a variety of fuels, the invention is especially adapted to the use of flammable gases, particularly natural gas, but others may be used including methane, synthetic gases or even hydrogen. Moreover, while the equipment and heat exchangers provided according to the invention are adapted to the heating of a variety of fluids, either liquid or gaseous, the invention is particularly well suited to the transfer of the available BTUs of the products of combustion to liquids and especially to the heating of water. For these reasons, the description given hereinafter refers to the utilization of the available BTUs in natural gas in the heating of water, but it is to be understood that these references are not to be construed in a limited sense.
One of the important objects of the present invention is the provision of a water heater employing a special combination of features including a combustion chamber and heat transfer tubes through which the combustion gases or products of combustion flow in a downward direction, while at the same time the conditions of heat transfer are established so as to reduce the temperature of the products of combustion to or below the dew point, provision further being made for downward delivery under the action of gravity of the condensate formed, thereby avoiding the necessity for the condensate and the flue gases to flow in the flue gas passages in opposite directions to each other. In accomplishing the foregoing, the present invention utilizes a blower effecting forced downward flow of the products of combustion from the combustion chamber through flue gas passages.
It is also contemplated according to the present invention to employ flue tubes for the flue gas and products of combustion, the flue tubes having their external surfaces in heat exchange relation to the water to be heated in a surrounding water flow space. In some instances the water flow space takes the form of annular passages surrounding the flue tubes, the passages being established by employment of water tubes surrounding the flue tubes, with appropriate tube sheets and water headers providing for circulation of the water in counterflow to the direction of flow of the gases through the inside flue tubes. This configuration is of particular importance in a heat exchanger as herein contemplated in which the temperature of the products of combustion is brought down below the dew point. The consequent development of the condensate results in development of certain acids having corrosive influence with respect to common types of metals employed in heat exchangers. In view of this, the invention contemplates employing highly acid resistant metals or surface treatment or coating of the metals to impart high acid resistance; and by confining the products of combustion to the interior of the inner tubes of the "tube-in-tube" heat exchangers disclosed, it is necessary to employ such special alloys or special surface treatments for the flue tubes only, instead of for both the inner and outer tubes, as would be needed in certain prior arrangements where the flue gases are passed through the tubular flow space between inner and outer tubes.
The invention also provides a novel form of gas and air admission means associated with the combustion chamber and providing increased efficiency in the intermixture of the gas and air being admitted into the combustion chamber.
It is another object of the invention to further enhance the efficiency of the heat transfer by employing a special form of helical fin within the flue tubes. Preferably these fins comprise individual twisted strips fitting into the interior of the flue tubes and providing for turbulence of the gas flow through the flue tubes. Preferably, such helical fins are metallurgically bonded to the interior surface of the flue tubes, and the fins not only provide the desired turbulence in the gas flow but also extensively increase the surface area within the flue tube providing for heat exchange from the products of combustion to the tube and thence through the tube wall to the surrounding water.
The invention also contemplates a system of automatic controls of novel form, as will be pointed out more fully hereinafter.
Still further the invention contemplates the employment of a novel form of gas discharge damper which is particularly adapted for use in combination with the downward flow of the flue gases as above described.
How the foregoing objects and advantages are attained, together with others which will be more fully developed hereinafter will be more fully apparent from the following description referring to the accompanying drawings illustrating four different embodiments of combustion and heat exchange devices according to the present invention.